Enabling error display in PHP via htaccess only

.htaccess:

php_flag display_startup_errors on
php_flag display_errors on
php_flag html_errors on
php_flag log_errors on
php_value error_log /home/path/public_html/domain/PHP_errors.log

I feel like adding more details to the existing answer:

# PHP error handling for development servers
php_flag display_startup_errors on
php_flag display_errors on
php_flag html_errors on
php_flag log_errors on
php_flag ignore_repeated_errors off
php_flag ignore_repeated_source off
php_flag report_memleaks on
php_flag track_errors on
php_value docref_root 0
php_value docref_ext 0
php_value error_log /full/path/to/file/php_errors.log
php_value error_reporting -1
php_value log_errors_max_len 0

Give 777 or 755 permission to the log file and then add the code

<Files php_errors.log>
     Order allow,deny
     Deny from all
     Satisfy All
</Files>

at the end of .htaccess. This will protect your log file.

These options are suited for a development server. For a production server you should not display any error to the end user. So change the display flags to off.

For more information, follow this link: Advanced PHP Error Handling via htaccess

php_flag display_errors on

To turn the actual display of errors on.

To set the types of errors you are displaying, you will need to use:

php_value error_reporting <integer>

Combined with the integer values from this page: http://php.net/manual/en/errorfunc.constants.php

Note if you use -1 for your integer, it will show all errors, and be future proof when they add in new types of errors.

If you want to see only fatal runtime errors:

php_value display_errors on
php_value error_reporting 4